Why does the value of g vary from place to place?

Answer 1

The actual gravitational force at the surface of the Earth (about 9.81 m/sec/sec) will vary as the distance from the Earth's center varies, and also due to variations in the density of the rock layers under any given location.

Answer 2

The value of "g" is technically the acceleration due to gravity at the surface of the Earth, but this question asks why the acceleration changes as one moves further away above the surface and as one moves "down" closer to the center of the Earth.

The short answer is that moving higher takes you further from the mass of the Earth and the force of gravity decreases, where as moving towards the center changes the distance you are from all the bits of mass of the Earth in a complicated way and the acceleration will perhaps increase, but will ultimately decrease to zero at the center of the Earth.

The gravitational force between two bodies decreases as the inverse square of the distance between two objects. The acceleration due to gravity therefore also decreases as the inverse square of the distance.

When one calculates the gravitational force caused by an extended object such as the Earth, one needs to add the forces of all the bits of matter that make up the Earth.

Outside: When one works out the mathematics, the force outside of a spherical mass is exactly the same as if the mass were concentrated at the center and not all spread about. Thus, for distances greater than the radius of the Earth, the acceleration due to gravity is proportional to the total mass of the Earth and decreases as the inverse square of the distance from the center of the Earth.

Inside: On the other hand, if you are inside of a spherical shell of mass, different parts of the shell are pulling in different directions and it all cancels out so there is no force at all.

Inside the Earth, the force of gravity may be viewed as the sum of two contributions. There is the force due to the mass that is closer to the center of the Earth than the point of observation and the contribution from the mass that is more distant from the center than your point of observation. The mass that is more distant provides zero net force. The mass that is nearer to the center gives the same force as if it were all concentrated at the center.

Now, here is the tricky part for the answer related to gravity inside the Earth. As your point of observation moves towards the center, more and more of the Earth's mass is outside of that distance from the center and therefore less mass is contributing to the force of gravity and so that tends to decrease the acceleration due to gravity. But, the mass that remains nearer to the center exerts a force as the inverse square of distance and that increases as you get closer to the center. These are competing effects, one increasing and one decreasing the acceleration of gravity. How ever the gravitational forces change as you near the center, they must all cancel out when you are exactly at the center and the net force at the center of the Earth must be zero. If (in your imagination) you were at the center of the Earth, you would be weightless.

The density of the Earth is not uniform and it is four or five times denser near the center than near the surface. By some estimates, the large quantity of mass near the center actually causes the acceleration due to gravity to increase slowly with depth as one goes down from the surface until one is about half way to the center and then it decreases more-or-less linearly for the last half until it is zero at the center.

(Technically, we need to emphasize that this is exactly correct only when the objects under discussion are spherical, but for the general purpose of discussing the acceleration due to Earth, it is close to being spherical.)

Answer 3

because it depends on your distance from the radius of earth

Answer 4

The value of "g" is the strength of the gravitational field, which depends on mass that attracts you, your distance to it.

Answer 5

The value of the acceleration of gravity g is equal to the radius of the earth are its surface . the value of gravity is inversally proportional to the square of distance between their masses . Its value decreases with the altitude .thus it does not remain every where and change place to place .